Technical Field
In its more general aspect, the present disclosure refers to a manufacturing method of a semi-finished product including a plurality of contact probes for a testing head, the probes being realized in substrate of the semi-finished product and being anchored thereto and the following description is carried out with reference to this application field with the only purpose to simplify its exposition.
Description of the Related Art
As it is well known, a testing head (or probe head) is essentially a device suitable to place a plurality of contact pads of a microstructure, in particular an electronic device that is integrated on a wafer, into electrical contact with corresponding channels of a testing machine performing the working test thereof, particularly the electrical one, or generically the test.
The test, which is performed on integrated devices, is particularly useful to detect and isolate defective devices yet in the manufacturing step. Therefore, the testing heads usually are used to electrically test the devices that are integrated on a wafer before cutting (singling) and assembling them inside a chip package.
A testing head usually includes a high number of contact elements or contact probes made of special alloys having good mechanical and electrical properties and being provided with at least one contact portion for a corresponding plurality of contact pads of a device under test.
A testing head comprising vertical probes, which is usually called “vertical probe head”, essentially includes a plurality of contact probes held by at least one pair of plates or guides, which are substantially plate-shaped and parallel to each other. Those guides are provided with specific holes and are arranged at a certain distance from each other in order to leave a free space or air gap for the movement and possible deformation of the contact probes. The pair of guides in particular include an upper guide and a lower guide, both provided with respective guide holes where the contact probes axially slide, the probes being usually made of special alloys having good electrical and mechanical properties.
The good connection between contact probes and contact pads of the device under test is guaranteed by pressing the testing head on the device itself, the contact probes, which are movable inside the guide holes made in the upper and lower guides, undergoing a bending inside the air gap between the two guides and a sliding inside those guiding holes during that pressing contact.
Moreover, the contact probes bending in the air gap can be assisted by means of a suitable configuration of the probes themselves or of their guides, as schematically shown in FIG. 1, where, for sake of illustration simplicity, only one contact probe of the plurality of probes usually included in a testing head has been depicted, the shown testing head being of the so-called shifted plates type.
In particular, in FIG. 1 a testing head 1 is schematically shown comprising at least one upper plate or guide 2 and one lower plate or guide 3, having respective upper guide hole 2A and lower guide hole 3A where the at least one contact probe 4 slides.
The contact probe 4 has at least one contact end or tip 4A. Here and in the following, the terms end or tip mean an end portion, not necessarily being sharp. In particular, the contact tip 4A abuts on a contact pad 5A of a device under test 5, realizing the electrical and mechanical contact between that device and a testing apparatus (not shown), the testing head 1 forming a terminal element thereof.
In some cases, the contact probes are fixedly fastened to the testing head at the upper guide: in such a case, the testing heads are referred to as blocked-probe testing heads.
Alternatively, testing heads are used having probes not fixedly fastened, but being interfaced to a board by means of a micro contact board: those testing heads are referred to as non-blocked probe testing heads. The micro contact board is usually called “space transformer” because, besides contacting the probes, it also allows spatially redistributing the contact pads made on it with respect to the contact pads of the device under test, in particular relaxing the distance constraints between the center of the pads themselves, namely with a space transformation in terms of distances between the adjacent pad centers.
In this case, as shown in FIG. 1, the contact probe 4 has a further contact tip 4B, which in this technical field is indicated as contact head, towards a plurality of contact pads 6A of that space transformer 6. The good electrical contact between probes and space transformer is guaranteed similarly to the contact with the device under test 5 by pressing the contact heads 4B of the contact probes 4 against the contact pads 6A of the space transformer 6.
As already explained, the upper 2 and lower 3 guides are suitably separated by an air gap 7 allowing the deformation of the contact probes 4 during the operation of the testing head 1 and guaranteeing that contact tip and contact head 4A and 4B of the contact probes 4 are contacting the contact pads 5A and 6A of the device under test 5 and space transformer 6, respectively. Clearly, the upper 2A and lower 3A guide holes must be sized in order to allow the contact probe 4 sliding therein.
It should be remembered that the proper operation of a testing head is essentially related to two parameters: the vertical movement, or overtravel, of the contact probes and the horizontal movement, or scrub, of the contact tips of those probes, where by “horizontal” it is meant a movement substantially coplanar to the device under test 5, and thus to the guides of the testing head 1, while by “vertical” it is meant a movement substantially orthogonal to the device under test 5 and to the guides of the testing head 1.
Therefore, these characteristics are to be evaluated and calibrated in the manufacturing step of the testing head, since the good electrical connection between probes and device under test should be always guaranteed.
It is also known to realize a contact probe 4 by means of a body 9A substantially extended in a longitudinal direction and made of a first conductive material, preferably a metal or a metal alloy, particularly a NiMn or NiCo alloy, as schematically shown in FIG. 2. Therefore, those contact probes 4 are arranged inside the testing head 1 with that longitudinal direction placed substantially vertically, i.e. perpendicularly to the device under test and to the guides.
The body 9A has a substantially central portion 8C having a preset length and two opposite ends or contact tips, precisely a contact end or contact tip 4A and a contact end or contact head 4B.
The contact tip 4A has a preset length 8A and it is intended to exert a pressing contact on a contact pad of a device under test (not shown, but anyway completely analogous to the contact pad 5A of the device under test 5 shown in FIG. 1) during the use of the contact probe 4.
Similarly, the contact head 4B in turn has a preset length 8B and instead it is intended to exert a pressing contact on a contact pad of a space transformer (not shown, but anyway completely analogous to the contact pad 6A of the space transformer 6 shown in FIG. 1), during the use of the contact probe 4, in particular in case of a non-blocked probe testing head.
As described for example in the Italian patent application No. MI2007A 002182 filed on 16 Nov. 2007 and granted on 23 Dec. 2010 with No. IT 1 383 883 on behalf of the same Applicant, it is known to coat the contact probe 4 with a layer 9B of a second conductive material, in particular having a hardness higher than that of the first conductive material realizing the body 9A. Preferably, the second conductive material is a metal or a metal alloy, in particular rhodium, gold, platinum or a palladium-cobalt PdCo alloy.
Moreover, as shown in FIG. 2, the central portion of the body 9A can be coated with a layer 9C too, in particular made of an insulating material, for example parylene.
In that way, the insulating coating realized by the layer 9C improves the electrical insulation of the contact probe 4 as a whole, avoiding short circuits in case of accidental contact between adjacent contact probes in the testing head 1.
The solution described in the above-mentioned Italian patent application in particular allows obtaining a greater hardness of the contact probe, at the same time guaranteeing the electrical insulation also in case of accidental contact with other adjacent contact probes.
However, that solution can reduce the electrical contact effectiveness between tips and heads of the contact probe and the respective contact pads.
In order to overcome that drawback, it is also known to coat the end portions of the contact probes, in particular at the contact tips and/or contact heads, using a highly conductive metal material, preferably gold.
Obviously, the involved dimensions as well as the cost of the involved materials make this coating operation extremely awkward.
Sometimes the contact probes are also subjected to common and often complex operations, the probes being placed and held to a dedicated support, which is usually called process frame. The probes held to the process frame then are subjected to one or more operations affecting them as a whole or at certain positions. Then, the contact probes should be removed from the process frame, in order to later proceed with their placement in a testing head.
Also in that case, the involved dimensions make the placing and holding operations of the contact probes to the process frame, and also their subsequent removal, complicated and expensive, especially in terms of manufacturing times and wastes.
US Patent Publication No. 2013/0069683 discloses a probe card manufacturing method wherein a plurality of contact probes is formed in a work-piece of a bulk conductive material by means of a reverse wire electrical discharge machining (R-WEDM) process. After the R-WEDM process, the contact probes remain attached to a common fabrication base, which is part of the original work-piece, and are then connected to a substrate. After the connection to the substrate, the fabrication base is then removed.
Moreover, US Patent Publication No. 2012/0176122 discloses a semi-finished product wherein contact probes are realized by filling with a metal material the opening of a mold that was previously realized by means of photolithographic techniques.